This invention relates generally to telescopic universal joints and more particularly to tripot type universal joints employed in automotive vehicle axle driveshafts and especially in front-wheel drive vehicles between the transaxle differential and the driving wheel. A telescopic constant velocity joint should not only transmit the torque at various speeds, angles and telescopic positions, but also prevent any vibrations of the engine from being transmitted through the joint and driveshaft to the driving wheel and the vehicle structure. In addition, when the universal joint operates at an angle, it should not produce any oscillating axial excitation which may be capable of initiating vibrations in the driveshaft or in the structure of the vehicle.
U.S. Pat. No. 3,125,870 granted to Michael Orain, Mar. 24, 1964, discloses a conventional telescopic tripot type universal joint of the prior art. These universal joints have been one of the best telescopic type universal joints available for isolating engine vibrations from the rest of the vehicle. However, because of their frictional operating characteristics, these conventional prior art tripot universal joints produce internally generated oscillating axial forces, which are related to the transmitted torque and the joint angle. During severe accelerations at low vehicle speeds, these cyclic axial forces can be of sufficient magnitude to produce a "shudder" type disturbance which has a frequency equal to three times the shaft speed.
The conventional tripot joint consists typically of an outer housing member with three equally spaced longitudinal drive channels driveably connected to an inner drive spider member through three trunnion mounted drive rollers which are capable of rotatable and slidable movement on their respective spider trunnions.
When the outer and inner drive members are aligned at zero degree joint angle and with axial stroking imposed on the joint under a torsional load, pure rolling motion occurs between the drive rollers and their corresponding drive channels. However, when such a joint is operated with the outer and inner drive members inclined to one another, the drive rollers are brought into an inclined relation with their respective drive channels so that each drive roller does not roll in the direction of its corresponding drive channel and consequently, some sliding or skidding along with rolling motion takes place between the two contacting surfaces. As the joint angle increases the amount of sliding also increases, while the amount of rolling decreases. As the joint rotates, this relative rolling-to-sliding relationship of each drive roller in its drive channel varies in an oscillating manner and produces a cyclic axial force along the rotational axis of the joint which has a frequency of three times the shaft speed.
In addition, as the joint rotates at an angle, relative endwise sliding movement of each drive roller on its corresponding spider trunnion also varies in a similar oscillating manner due to the joint's three per revolution orbiting characteristic. These effects are additive to the previously described cyclic axial force produced by the roller-to-drive channel contact relationship.